Virtualized serial attached SCSI adapter

ABSTRACT

A method, computer program product and computer system for the virtualization of an SAS storage adapter for logical partitions of a computer system, which includes providing a hypervisor, assigning a logical storage adapter to an operating system on one of the logical partitions, configuring the logical storage adapter using the hypervisor, and enabling data storage operations to use the logical storage adapter.

BACKGROUND

1. Technical Field

The present invention relates to storage adapters. More specifically, itrelates to the virtualization of an SAS (Serial Attached Small ComputerSystem Interface) adapter for logical partitions of a computer system.

2. Background Information

Large computer systems are usually partitioned into a number of logicalpartitions. Each logical partition represents a division of resources inthe system and operates as an independent logical system. An example oflogical partitions is the partitioning of a multiprocessor computersystem into multiple independent servers, each with it own processors,main storage, and I/O devices.

A typical resource that each logical partition requires is disk storage.Many systems utilize SAS devices to provide storage. SAS is a datatransfer technology designed to replace parallel SCSI (Small ComputerSystem Interface) with added performance, scalability and redundancy. Itcan provide SATA (Serial Advanced Technology Attachment) compatibilityand interoperability, cost-effective tiered storage deployments, andflexibility in disk drive and platform choices.

A drawback to current implementations of the logical partitions is thateach partition is required to have its own storage adapter. Hence, for alarge computer system, a large number of physical storage adapters areneeded, and, to provide the associated PCI (Peripheral ComponentInterconnect) or PCI Express adapter slots for these adapters, a largenumber of enclosures are also required, which lead to significantadditional expenses. Current implementations also require that eachpartition has its own storage devices, which results in an excess numberof storage devices and the corresponding enclosures used to house them.Moreover, each enclosure typically is packaged as a single SAS domain sothat the enclosure is limited to a single partition. Therefore, apartition that needs a single device (or a couple of devices) must bearthe cost of the complete enclosure that may have many empty deviceslots, which also causes a significant waste of resources.

SUMMARY

A method, computer program product and computer system for thevirtualization of an SAS storage adapter for logical partitions of acomputer system, which includes providing a hypervisor, assigning alogical storage adapter to an operating system on one of the logicalpartitions, configuring the logical storage adapter using thehypervisor, and enabling data storage operations to use the logicalstorage adapter.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a Host SAS Adapter configuration.

FIG. 2 is a block diagram showing components of one embodiment of thepresent invention.

FIG. 3 is a flowchart illustrating a read flow in one embodiment of thepresent invention.

FIG. 4 is a flowchart illustrating a write flow in one embodiment of thepresent invention.

FIG. 5 is a conceptual diagram of a computer system in which the presentinvention can be utilized.

DETAILED DESCRIPTION

The invention will now be described in more detail by way of examplewith reference to the embodiments shown in the accompanying Figures. Itshould be kept in mind that the following described embodiments are onlypresented by way of example and should not be construed as limiting theinventive concept to any particular physical configuration. Further, ifused and unless otherwise stated, the terms “upper,” “lower,” “front,”“back,” “over,” “under,” and similar such terms are not to be construedas limiting the invention to a particular orientation. Instead, theseterms are used only on a relative basis.

As will be appreciated by one skilled in the art, the present inventionmay be embodied as a system, method or computer program product.Accordingly, the present invention may take the form of an entirelyhardware embodiment, an entirely software embodiment (includingfirmware, resident software, micro-code, etc.) or an embodimentcombining software and hardware aspects that may all generally bereferred to herein as a “circuit,” “module” or “system.” Furthermore,the present invention may take the form of a computer program productembodied in any tangible medium of expression having computer-usableprogram code embodied in the medium.

Any combination of one or more computer usable or computer readablemedia may be utilized. The computer-usable or computer-readable mediummay be, for example but not limited to, an electronic, magnetic,optical, electromagnetic, infrared, or semiconductor system, apparatus,device, or propagation medium. More specific examples (a non-exhaustivelist) of the computer-readable medium would include the following: anelectrical connection having one or more wires, a portable computerdiskette, a hard disk, a random access memory (RAM), a read-only memory(ROM), an erasable programmable read-only memory (EPROM or Flashmemory), an optical fiber, a portable compact disc read-only memory(CD-ROM), an optical storage device, a transmission media such as thosesupporting the Internet or an intranet, or a magnetic storage device.Note that the computer-usable or computer-readable medium could even bepaper or another suitable medium upon which the program is printed, asthe program can be electronically captured, via, for instance, opticalscanning of the paper or other medium, then compiled, interpreted, orotherwise processed in a suitable manner, if necessary, and then storedin a computer memory. In the context of this document, a computer-usableor computer-readable medium may be any medium that can contain, store,communicate, propagate, or transport the program for use by or inconnection with the instruction execution system, apparatus, or device.The computer-usable medium may include a propagated data signal with thecomputer-usable program code embodied therewith, either in baseband oras part of a carrier wave. The computer usable program code may betransmitted using any appropriate medium, including but not limited towireless, wireline, optical fiber cable, RF, etc.

Computer program code for carrying out operations of the presentinvention may be written in any combination of one or more programminglanguages, including an object oriented programming language such asJava, Smalltalk, C++ or the like and conventional procedural programminglanguages, such as the “C” programming language or similar programminglanguages. The program code may execute entirely on the user's computer,partly on the user's computer, as a stand-alone software package, partlyon the user's computer and partly on a remote computer or entirely onthe remote computer or server. In the latter scenario, the remotecomputer may be connected to the user's computer through any type ofnetwork, including a local area network (LAN) or a wide area network(WAN), or the connection may be made to an external computer (forexample, through the Internet using an Internet Service Provider).

The present invention is described below with reference to flowchartillustrations and/or block diagrams of methods, apparatus (systems) andcomputer program products according to embodiments of the invention. Itwill be understood that each block of the flowchart illustrations and/orblock diagrams, and combinations of blocks in the flowchartillustrations and/or block diagrams, can be implemented by computerprogram instructions. These computer program instructions may beprovided to a processor of a general purpose computer, special purposecomputer, or other programmable data processing apparatus to produce amachine, such that the instructions, which execute via the processor ofthe computer or other programmable data processing apparatus, createmeans for implementing the functions/acts specified in the flowchartand/or block diagram block or blocks.

These computer program instructions may also be stored in acomputer-readable medium that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer-readablemedium produce an article of manufacture including instruction meanswhich implement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer orother programmable data processing apparatus to cause a series ofoperational steps to be performed on the computer or other programmableapparatus to produce a computer implemented process such that theinstructions which execute on the computer or other programmableapparatus provide processes for implementing the functions/actsspecified in the flowchart and/or block diagram block or blocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

The present invention provides a method to virtualize the SAS storageadapters and enclosures. This method can be implemented in hardware sothat no additional latency is incurred. In a large computer system, avirtualization platform, also known as the hypervisor, usually sits ontop of the physical hardware resources, and provides the function ofadministering resource management through the Hardware ManagementConsole (HMC). The hypervisor provides a level of abstraction to theoperating system. For example, from the perspective of the partition'soperating system, virtual hardware resources appear as if they belong tothat partition. The hypervisor controls partition access to the hardwareresources. Each operating system receives a logical storage adapter thatis a portion of the physical storage adapter. The hypervisor supportsthe configuration of a logical adapter, and exposes only those devicesto which this adapter is allowed access. The logical storage adapter istreated by the partition just like a dedicated physical storage adapter.

Therefore, in the present invention, only a single storage adapter isrequired to support multiple partitions. There is no need to purchase aseparate adapter for each logical partition of the system. Each logicaladapter works like a separate physical adapter, and no coordination orcommunication is required between the various device drivers oroperating system partitions. The partitions are also isolated from eachother. Thus, one partition will not corrupt or cause damage to anotherpartition, even if the device driver behaves improperly. The presentinvention enables zero-copy transfers of data with no interveningcopying of the data, just like well-implemented physical SAS adaptersdo. Moreover, the storage device enclosure is shared among separateoperating system partitions. Each device is seen by only a singlepartition and no partition communication is required to coordinateaccess. Furthermore, the present invention is fully interoperable withthe existing SAS products. A SAS expander is the item that providesconnectivity in the SAS fabric. It provides similar function as a switchin a network environment, and allows for one entity on the fabric totalk to many other entities. The present invention enables the physicalstorage adapter to appear as a logical SAS expander and a set of storageadapters. This greatly reduces the cost of the system.

In one embodiment of the present invention, a virtualized InfiniBandinterface is implemented as a software interface to the Host SAS adapterthat is presented to the partition. The Host SAS Adapter then maps thevirtual interface into physical SAS.

In order for a partition to communicate with a storage device throughthe InfiniBand interface, it must first create a work queue (WQ) thatconsists of a queue pair (QP). To execute an operation, it must place awork queue element (WQE) in the WQ. From there the operation ispicked-up for execution by the SAS adapter. Therefore, the WQ forms thecommunications medium between the partition and the SAS adapter,relieving the operating system from being involved. Each process maycreate one or more QPs for communications, where each QP has anassociated context. QPs can be implemented in hardware to off-load mostof the work from the CPU. Once a WQE has been processed properly, acompletion queue element (CQE) is created and placed in the completionqueue (CQ). Using the CQ for notifying the caller of completed WQEsreduces the interrupts that would be otherwise generated.

The implementation of one embodiment of the present invention isdescribed as follows.

Host SAS Adapter Configuration

Host SAS Adapter configuration is initiated from the HMC. Thisconfiguration is performed by the hypervisor so that the partitions donot need to be involved. During the configuration, the logical adaptersare created and assigned to partitions, and the devices are assigned tothe partitions that have access to them.

In SCSI, an initiator refers to an entity sending a command, and atarget is an entity (e.g. a disk driver) receiving the command. In oneembodiment of the present invention, each logical storage adapter actsas an initiator. Each logical storage adapter has its own initiator IDso that transactions on the SAS fabric can be executed properly. TheHost SAS Adapter configuration set up the fabrics-related parameter ofInitiator SAS address (I). The initiator address is a component of theInitiator/Target/Logic Unit Number Nexus (I_T_L Nexus, in which T is theTarget SAS Address and L is the Logic Unit Number (LUN), where a LUN isthe address assigned to a logical unit). A logical unit here is astorage entity that can include part of the storage on a disk drive, theentire storage on a disk drive, the total storage on multiple drives ina disk array, or any combination thereof.

FIG. 1 illustrates the Host SAS Adapter configuration. An I_T_L Nexus isautomatically generated and used during the execution of each command.For example, the I₀ _(—) T₀ _(—) L₀ Nexus refers to a mapping from theinitial SAS address I₀ to the target SAS address T₀, where the logicunit is L₀. After the Host SAS Adapter configuration, the I_T_L Nexusconfigurations appear like a physical SAS expander 102 and a set ofInitiators 101. Each virtual SAS initiator (I₀-I₃) has its own SASaddress and is logically independent on the bus.

Existing technology/protocols can be used to utilize the presentinvention with no further change required. The hypervisor can performfabric discovery and initialization using the standard SAS/SMP (SASManagement Protocol) protocols. These protocols are driven by thehypervisor, and they are not exposed to the partitions.

Logical SAS Adapter

Each logical operating system partition has its own Logical SAS Adapter.I₀, I₁, I₂ and I₃ in FIG. 1 are associated to four different logicaladapters. The system treats this logical adapter just like it wouldtreat a dedicated physical adapter.

In one embodiment of the present invention, a set of hypervisor callscan be defined to configure and program a logical adapter, through whichthe partition obtains Vital Product Data (VPD) information, which is acollection of configuration and informational data associated with theadapter and devices, as well as capabilities of the adapter. The virtualInfiniBand interface is employed to register memory, and to configureand use the QPs and other InfiniBand resources. For example, a QP can beused for normal command execution, while another QP is used forasynchronous events.

Memory Registration

When data storage is accessed, data is transferred directly to/frompartition memory to the storage device. The use of InfiniBand memoryregions enables direct data access. A partition first registers memoryregions reserved for the direct data transfer, e.g. using a hypervisorcall. The hypervisor then constructs all required structures so that thehardware can translate the address of a memory region into physicaladdresses and generate the correct transactions to the memory subsystem.

Memory regions are not explicitly used at the SAS interface level.Instead, an I_T_L_Q Nexus is used, where I=Initiator SAS Address,T=Target SAS Address, L=LUN and Q=Task Identifier. When an operation isstarted, the hardware generates an I_T_L_Q Nexus, and correlates it tothe correct offsets in the associated memory region(s). Then, if theoperation requests a data transfer, the hardware can correlate fromI_T_L_Q Nexus back to the correct memory region and to the correctphysical address, and perform the data transfer. The creation andmanagement of an I_T_L_Q Nexus can be handled completely by thehardware, and no software is involved.

The exact implementation of QP allocations in the partition isdetermined by the application. For example, for one application, one QPis allowed for each physical device. But in a different application, oneQP is allowed for a logical adapter. For illustration purpose, oneembodiment of the present invention allows one QP for each physicaldevice.

Therefore, each device allocates at least one QP 201, one CQ 202, oneEvent Queue (EQ) 203, and a number of memory regions 204, as illustratedin FIG. 2. Each QP 201 owns a send queue 206 and a receive queue 207.The partition 210 has access to the QP doorbell 205 for placing the sendand receive units of work on the QP 201. In the InfiniBand interface,these units of work are WQE's. The WQE's on the send and receive queuescontain scatter/gather type descriptors, each of which has a Key and aToken that are used to address a piece of partition storage where theunit of work to be sent or the storage to use for received data. TheQP's 201 also reference CQ's 202, which can be a single CQ, or a pair ofCQ's, one for the send queue and one for the receive queue. The CQ's 202reference the EQ 203 that is used to interrupt the partition (in 209) onthe completion of a work or in the event of an error. EQ 203 is the mostlimited resource of an adapter, so typically there is one EQ 203 per QP201.

Data storage access operations for one embodiment of the presentinvention are described with reference to FIG. 3-FIG. 4 in the followingparagraphs.

FIG. 3 is a flowchart illustrating a read flow in one embodiment of thepresent invention, which includes but is not limited to logical read andinquiry commands. The read flow starts and create memory regions fordevice status in state 300, then a WQE is placed on the receive queue toreceive the device status (state 301). In state 302, a memory regionwill be created via an Hcall as used for the Host Channel Adapter inInfiniBand. This memory region Hcall maps a virtual area in memory to aphysical address range so that the hardware can access data directlyto/from this memory region, and this memory region is reserved tocontain the read data received from the storage device. In state 303, aWQE is formed and placed on the send queue for the partition. The WQEcontains a request ID and a memory region descriptor for read data. Morespecifically, the WQE has a SCSI Command Descriptor Block (CDB) as wellas descriptor(s) (including address/length/key) for the memory regionwhich will contain the read data. The hardware sends the read command tothe device in state 304, and the storage device responds with data instate 305. Next in state 306, the physical adapter uses the I_T_L_QNexus to correlate this request back to the original WQE, and generatesthe actual physical address. Data is then stored into the data memoryregion. In state 307, the storage device sends device status (e.g. SCSIstatus and auto sense) to the host SAS adapter. And then in state 308,device status data is sent to memory region created for device status.The device status indicates the success or failure of the read, and, ifthe read fails, details of the failure. The request ID will be attachedto the original send WQE, so that the firmware can detect which requestthis device status is associated with. If the data is small, it can bereceived as “immediate” data, which means the data is actually placed inthe Receive WQE, rather than in the location as indicated by memoryregion descriptor. If the data is large (e.g. larger than 128 bytes),the data will be placed in the normal memory region that the memoryregion descriptor indicates. Note that data is not placed into the CQEbecause WQEs must complete in order, and this would preclude unorderedtagged command queueing and have a deleterious performance impact. Thedevice driver can then interpret the device status data.

FIG. 4 is a flowchart illustrating a write flow (i.e. a logical write)of one embodiment of the present invention. The logical write starts andcreate memory regions for device status in state 400. In state 401, aWQE element is placed on the receive queue to receive the device status.The application desired to write data to a storage device has stored thedata in the main system memory. In state 402, the memory regioncontaining the data is identified via an Hcall as for the Host ChannelAdapter in InfiniBand. This memory region Hcall maps a virtual area inmemory to a physical address range so the hardware can access datadirectly to/from the memory region. During the write flow, the SAShardware will read the data from this memory region and send it to thedevice. In state 403, a WQE is formed and placed on the send queue forthe partition. WQE contains a request ID and a memory region descriptorfor read data. This WQE will contain SCSI CDB as well as a descriptorfor the memory region which contains the data to be written. In state404, the hardware sends command to the device, and then in state 405,the physical adapter uses the I_T_L_Q Nexus to get memory region ID fromoriginal send WQE, which is then used to get physical address andreturns data from that address. During the write flow, the data insystem memory is unchanged. The I_T_L_Q Nexus is used to identify whichmemory locations are to serve as the source data for the write flow.This memory region is then read and sent to the device. The device thenstores the data. In state 406, the storage device sends device status(e.g. SCSI status and auto sense) to the Host SAS adapter. Next in state407, the device status is stored in the device status memory regiondescribed to receive queue WQE. The device status indicates the successor failure of the write, and, if the write fails, details of thefailure. The request ID will similarly be attached to the original sendWQE so that the firmware can detect which request this device status isassociated with. If the data is small, the data could be received as“immediate” data that is actually placed in the Receive WQE, rather thanin the location indicated by the memory region descriptor. However, ifthe data is large (e.g. larger than 128 bytes), this data can be placedin a normal memory region as indicated by the memory region descriptor.The device driver can then interpret the device status data.

FIG. 5 illustrates a computer system (502) upon which the presentinvention may be implemented. The computer system may be any one of apersonal computer system, a work station computer system, a lap topcomputer system, an embedded controller system, a microprocessor-basedsystem, a digital signal processor-based system, a hand held devicesystem, a personal digital assistant (PDA) system, a wireless system, awireless networking system, etc. The computer system includes a bus(504) or other communication mechanism for communicating information anda processor (506) coupled with bus (504) for processing the information.The computer system also includes a main memory, such as a random accessmemory (RAM) or other dynamic storage device (e.g., dynamic RAM (DRAM),static RAM (SRAM), synchronous DRAM (SDRAM), flash RAM), coupled to busfor storing information and instructions to be executed by processor(506). In addition, main memory (508) may be used for storing temporaryvariables or other intermediate information during execution ofinstructions to be executed by processor. The computer system furtherincludes a read only memory (ROM) 510 or other static storage device(e.g., programmable ROM (PROM), erasable PROM (EPROM), and electricallyerasable PROM (EEPROM)) coupled to bus 504 for storing staticinformation and instructions for processor. A storage device (512), suchas a magnetic disk or optical disk, is provided and coupled to bus forstoring information and instructions. This storage device is an exampleof a computer readable medium.

The computer system also includes input/output ports (530) to inputsignals to couple the computer system. Such coupling may include directelectrical connections, wireless connections, networked connections,etc., for implementing automatic control functions, remote controlfunctions, etc. Suitable interface cards may be installed to provide thenecessary functions and signal levels.

The computer system may also include special purpose logic devices(e.g., application specific integrated circuits (ASICs)) or configurablelogic devices (e.g., generic array of logic (GAL) or re-programmablefield programmable gate arrays (FPGAs)), which may be employed toreplace the functions of any part or all of the method as described withreference to FIG. 1-FIG. 4. Other removable media devices (e.g., acompact disc, a tape, and a removable magneto-optical media) or fixed,high-density media drives, may be added to the computer system using anappropriate device bus (e.g., a small computer system interface (SCSI)bus, an enhanced integrated device electronics (IDE) bus, or anultra-direct memory access (DMA) bus). The computer system mayadditionally include a compact disc reader, a compact disc reader-writerunit, or a compact disc jukebox, each of which may be connected to thesame device bus or another device bus.

The computer system may be coupled via bus to a display (514), such as acathode ray tube (CRT), liquid crystal display (LCD), voice synthesishardware and/or software, etc., for displaying and/or providinginformation to a computer user. The display may be controlled by adisplay or graphics card. The computer system includes input devices,such as a keyboard (516) and a cursor control (518), for communicatinginformation and command selections to processor (506). Such commandselections can be implemented via voice recognition hardware and/orsoftware functioning as the input devices (516). The cursor control(518), for example, is a mouse, a trackball, cursor direction keys,touch screen display, optical character recognition hardware and/orsoftware, etc., for communicating direction information and commandselections to processor (506) and for controlling cursor movement on thedisplay (514). In addition, a printer (not shown) may provide printedlistings of the data structures, information, etc., or any other datastored and/or generated by the computer system.

The computer system performs a portion or all of the processing steps ofthe invention in response to processor executing one or more sequencesof one or more instructions contained in a memory, such as the mainmemory. Such instructions may be read into the main memory from anothercomputer readable medium, such as storage device. One or more processorsin a multi-processing arrangement may also be employed to execute thesequences of instructions contained in main memory. In alternativeembodiments, hard-wired circuitry may be used in place of or incombination with software instructions. Thus, embodiments are notlimited to any specific combination of hardware circuitry and software.

The computer code devices of the present invention may be anyinterpreted or executable code mechanism, including but not limited toscripts, interpreters, dynamic link libraries, Java classes, andcomplete executable programs. Moreover, parts of the processing of thepresent invention may be distributed for better performance,reliability, and/or cost.

The computer system also includes a communication interface coupled tobus. The communication interface (520) provides a two-way datacommunication coupling to a network link (522) that may be connected to,for example, a local network (524). For example, the communicationinterface (520) may be a network interface card to attach to any packetswitched local area network (LAN). As another example, the communicationinterface (520) may be an asymmetrical digital subscriber line (ADSL)card, an integrated services digital network (ISDN) card or a modem toprovide a data communication connection to a corresponding type oftelephone line. Wireless links may also be implemented via thecommunication interface (520). In any such implementation, thecommunication interface (520) sends and receives electrical,electromagnetic or optical signals that carry digital data streamsrepresenting various types of information.

Network link (522) typically provides data communication through one ormore networks to other data devices. For example, the network link mayprovide a connection to a computer (526) through local network (524)(e.g., a LAN) or through equipment operated by a service provider, whichprovides communication services through a communications network (528).In preferred embodiments, the local network and the communicationsnetwork preferably use electrical, electromagnetic, or optical signalsthat carry digital data streams. The signals through the variousnetworks and the signals on the network link and through thecommunication interface, which carry the digital data to and from thecomputer system, are exemplary forms of carrier waves transporting theinformation. The computer system can transmit notifications and receivedata, including program code, through the network(s), the network linkand the communication interface.

It should be understood, that the invention is not necessarily limitedto the specific process, arrangement, materials and components shown anddescribed above, but may be susceptible to numerous variations withinthe scope of the invention.

1. A method for virtualizing an SAS (Serial AttachedSmall-Computer-System-Interface) storage adapter, connected to a storagedevice, for logical partitions of a computer system, comprising:assigning, using a hypervisor, a logical storage adapter to a selectedone of the logical partitions; configuring the logical storage adapter,using the hypervisor, and assigning an initiator SAS address to thelogical storage adapter; generating an Initiator/Target/Logic unitnumber nexus (I_T_L nexus) that correlates the initiator SAS address, atarget SAS address of the storage device, and a logic unit number thatis an address of a storage entity of the storage device; and enablingdata storage operations to access the storage entity through the logicalstorage adapter using the generated nexus.
 2. The method of claim 1,wherein the assigning a logical storage adapter includes assigning aplurality of logical storage adapters each for one of the logicalpartitions; and the configuring the logical storage adapter includesimplementing a logical SAS expander and assigning a plurality ofinitiators each for one of the logical storage adapters.
 3. The methodof claim 1, wherein the logical storage adapter provides an InfiniBandprogramming interface to the selected logical partition.
 4. The methodof claim 1, wherein the configuring comprises memory registration thatcreates and manages a memory region used for data access.
 5. The methodof claim 1, wherein the data storage operations comprise a readoperation that places data directly into a memory of the selectedlogical partition.
 6. The method of claim 1, wherein the data storageoperations comprise a write operation that retrieves data directly froma memory of the selected logical partition.
 7. The method of claim 1,wherein the hypervisor receives device command completion statusinformation and places the information directly into a memory regionidentified through one of the data storage operations.
 8. A computerprogram product for virtualizing a SAS (Serial AttachedSmall-Computer-System-Interface) storage adapter, connected to a storagedevice, for logical partitions of a computer system, the computerprogram product comprising: a computer usable medium having computerusable program code embodied therewith, the computer usable program codecomprising: instructions to assign, using a hypervisor, a logicalstorage adapter to a selected one of the logical partitions;instructions to configure the logical storage adapter, using thehypervisor, and to assign an initiator SAS address to the logicalstorage adapter; instructions to generate an Initiator/Target/Logic unitnumber nexus (I_T_L nexus) that correlates the initiator SAS address, atarget SAS address of the storage device, and a logic unit number thatis an address of a storage entity of the storage device; andinstructions to enable data storage operations to access the storageentity through the logical storage adapter using the generated nexus. 9.The computer program product of claim 8, wherein the instructions toassign a logical storage adapter includes instructions to assign aplurality of logical storage adapters each for one of the logicalpartitions; and the instructions to configure the logical storageadapter includes instructions to implement a logical SAS expander and toassign a plurality of initiators each for one of the logical storageadapters.
 10. The computer program product of claim 8, wherein thelogical storage adapter provides an InfiniBand programming interface tothe selected logical partition.
 11. The computer program product ofclaim 8, wherein the instructions to configure comprise instructions formemory registration that creates and manages a memory region used fordata access.
 12. The computer program product of claim 8, wherein thedata storage operations comprise a read operation that places datadirectly into a memory of the selected logical partition.
 13. Thecomputer program product of claim 8, wherein the data storage operationscomprise a write operation that retrieves data directly from a memory ofthe selected logical partition.
 14. The computer program product ofclaim 8, wherein the hypervisor receives device command completionstatus information and places the information directly into a memoryregion identified through one of the data storage operations.
 15. Acomputer system comprising: a processor; a memory operatively coupledwith the processor; a storage device operatively coupled with theprocessor and the memory; and a computer program product forvirtualizing a SAS (Serial Attached Small-Computer-System-Interface)storage adapter, connected to a storage device, for logical partitionsof a computer system, the computer program product comprising: acomputer usable medium having computer usable program code embodiedtherewith, the computer usable program code comprising: instructions toassign, using a hypervisor, a logical storage adapter to a selected oneof the logical partitions; instructions to configure the logical storageadapter, using the hypervisor, and to assign an initiator SAS address tothe logical storage adapter; instructions to generate anInitiator/Target/Logic unit number nexus (I_T_L nexus) that correlatesthe initiator SAS address, a target SAS address of the storage device,and a logic unit number that is an address of a storage entity of thestorage device; and instructions to enable data storage operations toaccess the storage entity through the logical storage adapter using thegenerated nexus.
 16. The computer system of claim 15, wherein theinstructions to assign a logical storage adapter includes instructionsto assign a plurality of logical storage adapters each for one of thelogical partitions; and the instructions to configure the logicalstorage adapter includes instructions to implement a logical SASexpander and to assign a plurality of initiators each for one of thelogical storage adapters.
 17. The computer system of claim 15, whereinthe logical storage adapter provides an InfiniBand programming interfaceto the selected logical partition.
 18. The computer system of claim 15,wherein the instructions to configure comprise instructions for memoryregistration that creates and manages a memory region used for dataaccess.
 19. The computer system of claim 15, wherein the data storageoperations comprise a read operation that places data directly into amemory of the selected logical partition.
 20. The computer system ofclaim 15, wherein the data storage operations comprise a write operationthat retrieves data directly from a memory of the selected logicalpartition.
 21. The computer system of claim 15, wherein the hypervisorreceives device command completion status information and places theinformation directly into a memory region identified through one of thedata storage operations.
 22. The method of claim 1, wherein the I_T_Lnexus is generated using standard SAS/SMP (SAS Management Protocol)protocols.
 23. The computer program product of claim 8, wherein theI_T_L nexus is generated using standard SAS/SMP (SAS ManagementProtocol) protocols.
 24. The computer system of claim 15, wherein theI_T_L nexus is generated using standard SAS/SMP (SAS ManagementProtocol) protocols.